1. Field of the Invention
The present invention relates to a differential gear assembly for use in a vehicle or the like.
2. Description of the Prior Art
Generally, a differential gear assembly used in a vehicle is prepared for occurrence of slipping or skidding of one tire so as to provide a sufficient rotation force to the other tire which is not slipped. For example, such a differential gear assembly is disclosed in Japanese Laid-Open Patent Publication No. (Kokai) 97846/1984.
The differential gear assembly disclosed in the above-referenced publication comprises a case having a cylindrical bore. The bore is provided at its circumference with a plurality of receptacle grooves which are arranged in pairs and extend along an axial direction of the bore. Each of the receptacle grooves has a cylindrical inner wall. Within the bore, left and right side gears are rotatably arranged and coupled to left and right torque shafts, respectively. The receptacle grooves in each pair receive first and second pinion gears in such a manner that the first and the second pinion gears are rotatable and extend in parallel to the left and the right side gears. The first pinion gear comprises first and second gear portions while the second pinion gear comprises third and fourth gear portions. The left side gear is engaged with a part of the first gear portion of the first pinion gear while the right side gear is engaged with a part of the fourth gear portion of the second pinion gear. The other part of the first gear portion of the first pinion gear is engaged with the third gear portion of the second pinion gear while the other part of the fourth gear portion of the second pinion gear is engaged with the second gear portion of the first pinion gear.
A pair of flat side plates are arranged axially outwardly of the first and the second pinion gears to define axial positions of the pinion gears. The flat side plates cover the opposite end faces of the differential gear assembly.
The above-mentioned differential gear assembly is designed so that friction is caused between the pinion gears and the receptacle grooves when the first and the second pinion gears are rotated within the receptacle grooves and that the pinion gears are engaged with each other. Accordingly, when the vehicle is turned with both tires kept in tight contact with the ground, differential operation enables differential rotation dependent upon a difference in rotation speed between the both tires. On the other hand, when one tire is slipped, the differential operation is restricted or limited by the friction caused in the receptacle grooves. It is therefore possible to prevent the loss of the rotational force transmitted to the other tire which is not slipped. Thus, an excellent road ability can be assured even in a rough road.
However, the receptacle grooves receiving gear portions of the first and the second pinion gears do not support the entire periphery of the gear portions. In this connection, each pinion gear tends to be dislocated towards the other pinion gear or towards the side gear. Accordingly, proper engagement between the pinion gears could not always be maintained. This results in insufficiency in durability and quietness. It is noted that restriction of the differential operation is related to the friction between the receptacle grooves and the pinion gears. Accordingly, it is necessary to provide a sufficient contact area between the pinion gears and the receptacle grooves. This results in an increase of the axial length, in combination with the instability in positions of the center axes of the pinion gears.